This invention relates to the metallization of insulating substrates, and, more particularly, to the electrodeposition of conducting coatings on insulating substrates. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
There are many electronic applications that require the metallization of insulating, i.e., nonconducting substrates, e.g., shielded enclosures, thin film conductors, printed circuit boards, VLSI circuits, etc. Conventional electroplating processes can not be initiated on insulating substrates since these processes require the presence of a conductive substrate surface. Accordingly, electroless processes are used to deposit at least an initial film of conductive material and the resulting film serves as a substrate for subsequent electroplating.
Conventional electroless deposition uses a chemical process for forming a metal on an insulating substrate. The chemical processes generally require the use of environmentally and physically hazardous chemicals, such as formaldehyde, and the use of precious metals, such as palladium, as a catalyst for the chemical reaction. Such processes are in widespread use in the production of circuit boards for use in electronic components.
An alternate process is described in PCT Application No. PCT/EP89/00204, Publication No. WO89/08375, published Sep. 8, 1989. Conducting polymers are applied to the substrate in various processes wherein a monomer is applied to a substrate and thereafter oxidized to form a conducting polymer. A metal is then electrodeposited over the conducting polymer. However, this and other related processes use a multi-step process to form the conducting layer whereby the underlying substrate is moved from one chemical bath to another to complete the polymerization process.
To provide an attractive alternative to conventional electroless metal deposition, a conducting-polymer-based process should (a) not involve hazardous chemicals, (b) use a simple polymer coating process, (c) provide a polymer film with sufficient conductivity for subsequent metal electrodeposition, (d) provide adequate peel strength for the deposited metal, (e) enable through-hole plating, and (f) use inexpensive chemicals. A suitable commercial process would also be continuous and have a minimum number of process steps. These concerns are addressed by the present invention wherein a conductive-polymer-based process includes a single step, continuous process for forming the polymer that is readily adaptable to a manufacturing operation.
Accordingly, it is an object of the present invention to electroplate insulating substrates in a manufacturing process without forming a precursor metal film by a chemical process.
It is another object of the present invention to form a conducting polymer onto an insulating substrate in a single bath.
It is yet another object of the present invention to electroplate a metal onto a substrate coated with a conducting polymer.
Yet another object of the present invention is to provide a generally continuous process for forming films of conducting polymer precoats for use in a metal electrodeposition process.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.